The invention relates to a precision current-source arrangement for generating a plurality of currents whose values are proportioned accurately relative to each other, which arrangement comprises
a current-distribution circuit for generating a plurality of currents of substantially equal values, and
a permutation circuit for transferring the currents from the current-distribution circuit to the outputs of the permutation circuit in accordance with a cyclic permutation, so that the currents available on said outputs have average values which are proportioned accurately relative to each other and exhibit a ripple whose components depend on the difference of the currents from the current-distribution circuit.
Such a precision current-source arrangement may be used in, for example, a digital-to-analog converter which requires a binary weighted series of currents whose values are proportioned accurately relative to each other.
Such a precision current-source arrangement, employing the dynamic permutation principle, is known from U.S. Pat. No. 3,982,172 and from U.S. Pat. No. 4,125,803. These arrangements employ a current-distribution circuit which supplies a plurality of currents whose values are only substantially equal to each other due to the limited accuracy of the integration process. A permutation circuit transfers these currents to its outputs in accordance with a cyclic permutation. Each output current comprises a direct current of the desired value and, superimposed on it, a ripple whose components depend on the mutual differences of the currents from the current-distribution circuit. The value of the direct current on the output is equal to the average value of the currents from the current-distribution circuit. Averaged over the cycle time of the permutation circuit, the value of the ripple is zero. The ripple can be filtered out by arranging a filter capacitor on each output of the permutation circuit.
A disadvantage of the use of such filter capacitors is that because of their large values, they cannot be integrated but have to be added to the integrated circuit as external components. This requires additional connection pins on the integrated circuit, which entails additional costs. For example, in the case of a 16-bit digital-to-analog converter employing such a precision current-source arrangement, 16 additional connection pins are required.